Halfpenny threw the ball backward but it went forward. "An object in motion stays in motion," wrote Newton, "with the same speed and in the same direction unless acted upon by an unbalanced force." Fall out of a moving car and you will hit the ground not at the spot at which you left the vehicle but, depending on its speed, some metres in front. Take a running jump off the back of a moving truck and, again, you fall forward of the point you left it.
Law 12 is simple in its definition: "A throw forward occurs when a player throws or passes the ball forward." 'Forward' means towards the opposition's dead ball line." The one stated exception to the rule is if a ball is not thrown forward but hits a player or the ground and then bounces forward.
The Australian Rugby Union issued a video seven years ago explaining why momentum meant that a pass looking forward was illusory and that spectators who yelled at a referee to blow up after the player passing the ball was tackled immediately after releasing it were wrong: it merely looked forward because by the time the receiver caught it, he was well in front of the prone passer whereas had both continued their runs unchecked, he would have remained behind.
The video also showed how, when a player is running at pace, if he delivered a forward pass it would almost be impossible for the receiver to catch the ball because it would be so far in front of him. The International Rugby Board issued a clarification to its throw forward regulation before the 2011 World Cup, emphasising the points raised in the video, and they have been observed by referees and television match officials since.